Solid state phase reversal protector for three phase hoist motor



July 30, 1 0. M. RAGER, JR 3,395,324

SOLID STATE PHASE REVERSAL PROTECTOR FOR THREE PHASE HOIST MOTOR Filed Nov. 12, 1965 2 Sheets-Sheet 1 FIG.

INVENTOR.

DONALD M. RAGER, JR.

y 30 1968 o. M. RAGER, JR 3,395,324

SOLID STATE PHASE REVERSAL PROTECTOR FOR THREE PHASE HOIST MOTOR Filed Nov. 12, 1965 2 Sheets-Sheet 2 z FIG. 20 I 2 FIG. 2b

INVENTOR.

DONALD M. RAGER, JR.

ATTORNEYS United States Patent Filed Nov. 12, 1965, Ser. No. 507,294 8 Claims. (Cl. 318-202) This invention relates to safety devices and pertains, more particularly, to an assembly including a phase-sensitive device which prevents improper operation in the event that the input terminals of the assembly are improperly connected to an external source of polyphase power.

The present invention is particularly adapted for, although not necessarily limited to, the control circuit for an electric hoist utilizing a 3-phase motor as its source of power. Such an electric hoist assembly will include, in addition to the 3-phase motor, a control assembly for effecting relatively opposite directions of rotation of the motor for correspondingly raising or lowering a load associated with a hoist. If the input terminals to the hoist are improperly connected to a 3-phase circuit, the up push-button control for the hoist will cause load lowering whereas the down push-button will cause load raising. This of course is not only inconvenient but might give rise to a dangerous situation. Moreover, electric hoists are frequently provided with limit switches which themselves operate as safety devices to prevent a load from being raised or lowered too far. Under the circumstances outlined, that is with the input terminals improperly connected, the limit switches will be ineffective since the load raising limit switch is effective only in conjunction with the up button and the load lowering limit switch is effective only in association with the down button so that if the connections are relatively reversed, the load limit switches will be ineffective to break the appropriate circuits and stop operation of the hoist device.

Thus, it is of primary concern in connection with this invention to provide a phase-sensitive safety device for use in association wtih electric hoist assemblies utilizing a 3-phase motor which will disable and prevent operation of the hoist device unless the input terminals are properly phased with relation to the power source.

It is also an object of this invention to provide an assembly of the aforementioned character wherein the safety device employs a combination of an A-C switch having a control or gate electrode which, unless energized with a voltage exceeding a predetermined value, will permit the switch to remain in normally open position, and in combination therewith, a control transformer and associated circuitry for providing the predetermined voltage on the gate or control electrode only if the input terminals of the assembly are properly connected to an external source of 3-phase power.

Further, it is an object of this invention to provide a phase-sensitive device in accordance with the preceding paragraph which is of relatively simple yet effective construction and which is characterized by a very large difference in output voltage on the secondary of the control transformer in response to proper and improper input terminal connections to the external source of 3-phase power whereby a very definite control action is achieved.

Other objects and advantages of the invention will appear from the specification hereinafter and the accompanying drawing, wherein:

FIG. 1 is the electrical circuit illustrating the principles of the present invention;

FIG. 2a is a diagram illustrating the phase relations between the currents and voltages in the two sections of the control transformer when the input terminals are improperly connected to the external source of 3-phase power; and

FIG. 2b is a view similar to FIGURE 2a but showing the phase relations when the input terminals are properly connected to the external source of 3-phase power.

With reference now more particularly to FIGURE 1, the reference characters 10, 12 and 14 indicate the three input terminals of an electric hoist assembly utilizing a 3-phase motor 16 as the power source and which terminals 10, 12 and 14 are adapted to be connected to an external source of 3-phase power as will be well understood by those skilled in the art. The motor 16 is characterized by the fact that it will rotate in relatively opposite directions when the phase input connections thereto are relatively reversed and advantage is taken of this fact for providing manual control for raising and lowering the load associated with the hoist assembly. However, in view of the fact that the push-button controls are marked and intended for operation in only one of the two relatively reversed directions of the motor 16, it becomes important that the input terminals 10, 12 and 14 be properly connected to the external source of power to provide the corresponding proper control operations. In many cases, an electric hoist will be moved from time to time and it is perfectly possible that the input terminals will be improperly connected to the external power source, thus giving rise to an undesirable if not dangerous situation. The reason for this is that the normal manual control for the electric hoist motor 16 includes an up switch 18 and a down switch 20 which operate to control respective relays 22 and 24 whose associated switches operate to reverse the connections of the motor to the input terminals 10, 12 and 14.

If the input terminals 10, 12 and 14 have been improperly phased to the external power source to begin with, the up switch 18 will cause load lowering whereas the down switch 20 will cause load raising. As a consequence, it is easily possible for an accident to occur if the operator is unaware of the improper input terminal connections as aforesaid.

Moreover, electric hoists usually include limit switches such as the normally closed switches 26 and 28, the former of which is automatically operated as soon as the load has been raised too high and the latter of which is automatically operated as soon as the load is lowered too far. If, as aforesaid, the input terminals are improperly connected to the external source of power, depression of the manual control switch 18 will cause load lowering, under which circumstances the load lowering limit switch 28, even when actuated, will be ineffective to cease operation of the motor 16. The same will be true insofar as the load raising limit switch 26 is concerned.

FIGURE 1 shows a conventional circuitry for powering the manual switches 18 and 20 and this is accomplished from a secondary winding 30 of an input transformer T which is connected to the aforementioned input terminals 10, 12 and 14 substantially as is shown. According to the present invention, however, instead of directly connecting the transformer secondary 30 to the circuit including the switches 18 and 20, there is interposed therein an A-C switch 32 which switch is characterized by having a control or gate electrode 34 which allows the switch to remain in its normally open condition until such time as a small turn-on voltage is present at the gate or control electrode 34.

For this purpose, I prefer to use a bi-directional triode switch such 'as a Triac switch, manufactured by the General Electric Company.

For the purpose of providing the appropriate turn-on voltage to the control electrode 34 only when the input terminals 10, 12 and 1-4 have been correctly phased to the external power source, the transformer T is provided, the same being characterized by having a tapped primary winding as shown which, in effect, divides the primary 3- into three inductance coil circuits, one including the winding section L the second including the winding section L and the third including the combined sections L and L comprising the entire primary winding. The section L is connected across one pair of the input terminals by means of the resistor R the capacitor C and the resistor R whereas the second section L is connected across a different pair of the input terminals through the aforementioned resistor R and a further resistor R substantially as is shown in FIGURE 1. By way of example, the circuit components may have the following relative values or others depending on line frequency. For 60 -c.p.'s., the values may be as follows:

R 20K R 66K C microfarads .047 L 1.16H L 9.2H

The circuit including the coil section L is characterized by having a high capacitive reactance to resistance ratio so that the current in the coil L due to the impressed voltage lags the impressed. voltage by approximately 60, substantially as is shown in FIGURES 2a and 2b. The inductive reactance of the circuit of the coil L on the other hand, is very small with respect to the sum of the resistors R and R so that the current I in the coil section L due to the impressed voltage E is substantially in phase with the impressed voltage, substantially as is shown in FIGURES 2a and 2b. Thus, considering FIGURES 2a and 2b, when the input terminals are connected so that the voltages E and B are related in phase as shown in FIGURE 2a, the currents I and 1 will be substantially 180 apart, as shown, so that there is very little resultant current. At the same time, it will be noted that the impedance in the coil circuit which includes both sections L and L is very high so that the current 1;, will always be very small so that the net resultant current due to I I and 1;, with the phase relation existing as shown in FIG- URE 2a will be so small as to produce insufficient voltage in the secondary 36 of the transformer T to turn the A-C switch on. If, however, the input terminals are correctly connected, the phase relationship shown in FIG- URE 2b will exist, in which the current I resultant from the currents I and I in substantial so that the secondary 32 will produce sufiicient voltage to turn the A-C switch 3 on.

As has been mentioned, it is desirable to provide a large ratio between resultant currents as between the properly and improperly phased relation at the input termi-nals and to enhance this effect, it will be noted that the transformer of primary section L is wound with fewer turns that the primary section L and that the current in the circuit including the two sections L and L is always very small. This combination provides the optimum amount of reactance to resistance ratio giving a resultant optimum amount of phase shift with associated broad tuning characteristics for greatest cancellation in the outof-phase condition, to fully turn on the least sensitive A-C switch 32 at low line voltages and low environmental temperatures. The device specifically shown and tabulated as above is capable of functioning over an extremely broad line voltage range (190-528 volts RMS). The power dissipation is approximately three watts at 415 volts line and less than /2 watt at 240 volts line and requires no change in circuitry when connecting the hoist for either 240, 415 or 528 volt service, connecting the hoist for line voltages between 190 and 528 volts RMS.

The laminations and steel characteristic of the core of the transformer T is chosen to provide a BH curve that permits the core to increasingly saturate at the higher line voltages thereby preventing over-driving the bi-directional triode switch 32 at these higher line voltages,

thereby making it unnecessary to change connections when going to higher line voltages.

Whereas only one form of the invention has been illustrated and described in detail hereinabove, it will be understood that various changes may be made therein without departing 'from the spirit of the invention or the scope of the following claims.

I claim:

1. A control assemblycomprising', in combination,

a polyphase motor adapted to be actuated in relatively reversed directions,

terminal means for connection to an external polyphase control means for said motor including a transformer having a primary connected to said terminal means and a secondary, a first switch in the transformer secondary circuit for connecting said motor to said terminal means to operate said motor in one direction and a second switch in the transformer secondary circuit for connecting said motor to said terminal means to operate said motor in the opposite direction,

and a safety device for energizing said control means only when said terminal means is connected to an external power source in such relation as to cause the aforesaid directional movements of said motor in response to actuating of the corresponding switch, said safety device including a normally open A-C switch for connecting said first and second switches to said transformer secondary and having a control electrode adapted to close the AC switch only in response to the presence of an A-C voltage exceeding a predetermined value, a transformer having a primary winding and a secondary winding in which the secondary winding is coupled to said control electrode of the A-C switch, said primary winding having two sections, means coupling the two sections of the primary winding to dilferent pairs of electrodes of said terminal means, and impedance means associated with one of said sections for causing the currents in the two sections to .be (a) substantially in bucking relation when the terminal means is incorrectly connected to an external power source and (b) in additive relation when the terminal means is correctly connected to an external power source.

2. The assembly as defined in claim 1 wherein said control means includes a limit switch associated with one 0 said first and second switches.

3. The assembly as defined in claim 2 wherein said impedance means comprises a series R-C circuit connected to said one section.

4. The assembly as defined in claim 1 wherein said impedance means comprises a series R-C circuit connected to said one section.

5. The assembly as defined in claim 1 wherein the number of turns in said one section is much less than the number of turns in the other section, said sections having resistance in their circuit connection to the terminal means in which the resistance associated with said one section is much less than the resistance associated with said other section.

6. The assembly as defined in claim 1 wherein the current in said one section lags the impressed voltage therein by about 60 and the current in the other section is substantially in phase with the voltage impressed therein.

7. A hoist assembly comprising, in combination,

a load engaging device,

a reversible, 3-phase motor for selectively operating said load engaging device in load raising and load lowering directions,

terminal means for energizing said motor and adapted for external connection to a source of 3-phase power,

a control assembly for said motor including a first manually operated switch for operating said motor in load raising direction and a second manually operated switch for operating said motor in load lowering direction,

a safety device comprising a limit switch connected in circuit with one of said manually operated switches and operable to terminate movement of said load engaging means in that direction corresponding to the intended direction of movement, as aforesaid, of the manually operated switch with which it is associated only while said one manually operated switch is operated,

and phase-sensitive means coupled to said terminal means for coupling said terminal means to said motor through said manually actuated switches only in response to external power source connections to said terminal means as would cause load raising movement of said load engaging means when said first manually actuated switch is actuated and load lowering when said second manually actuated switch is actuated.

8. The assembly defined in claim 7 wherein said phase sensitive means comprises a normally open A-C switch having a control electrode for closing the A-C switch in response to the presence of a predetermined voltage thereon, a transformer having a primary winding and a secondary winding coupled to said control electrode, said primary winding having first and second sections coupled to different pairs of electrodes of said terminal means, an R-C combination connected in circuit with said first section and resistance means connected in circuit with said second section, the impedance of the circuit of said first section being such as to cause the current to lag the voltage by about 60, while the impedance of the circuit of said second section being such as to cause the current and voltage to be substantially in phase.

References Cited UNITED STATES PATENTS 2,975,334- 3/1961 Callan 317-48 3,039,023 6/ 1962 Thompson 317-48 3,218,485 11/1965 Takai 30712.7

ORIS L. RADER, Primary Examinler. G. RUBINSON, Assistant Examiner. 

1. A CONTROL ASSEMBLY COMPRISING, IN COMBINATION A POLYPHASE MOTOR ADAPTED TO BE ACTUATED IN RELATIVELY REVERSED DIRECTIONS, TERMINAL MEANS FOR CONNECTION TO AN EXTERNAL POLYPHASE SOURCE, CONTROL MEANS FOR SAID MOTOR INCLUDING A TRANSFORMER HAVING A PRIMARY CONNECTED TO SAID TERMINAL MEANS AND A SECONDARY, A FIRST SWITCH IN THE TRANSFORMER SECONDARY CIRCUIT FOR CONNECTING SAID SAID MOTOR TO SAID TERMINAL MEANS TO OPERATE SAID MOTOR IN ONE DIRECTION AND A SECOND SWITCH IN THE TRANSFORMER SECONDARY CIRCUIT FOR CONNECTING SAID MOTOR TO SAID TERMINAL MEANS TO OPERATE SAID MOTOR IN THE OPPOSITE DIRECTION, 